The Linux Programming Interface

Monitoring Child Processes 543

Listing 26-1: Creating and waiting for multiple children

––––––––––––––––––––––––––––––––––––––––––––––––––––– procexec/multi_wait.c
#include <sys/wait.h>
#include <time.h>
#include "curr_time.h" / Declaration of currTime() /
#include "tlpi_hdr.h"

int
main(int argc, char argv[])
{
int numDead; / Number of children so far waited for /
pid_t childPid; / PID of waited for child */
int j;

if (argc < 2 || strcmp(argv[1], "--help") == 0)
usageErr("%s sleep-time...\n", argv[0]);

setbuf(stdout, NULL); / Disable buffering of stdout /

for (j = 1; j < argc; j++) { / Create one child for each argument /
switch (fork()) {
case -1:
errExit("fork");

case 0: / Child sleeps for a while then exits /
printf("[%s] child %d started with PID %ld, sleeping %s "
"seconds\n", currTime("%T"), j, (long) getpid(), argv[j]);
sleep(getInt(argv[j], GN_NONNEG, "sleep-time"));
_exit(EXIT_SUCCESS);

default: / Parent just continues around loop /
break;
}
}

numDead = 0;
for (;;) { / Parent waits for each child to exit /
childPid = wait(NULL);
if (childPid == -1) {
if (errno == ECHILD) {
printf("No more children - bye!\n");
exit(EXIT_SUCCESS);
} else { / Some other (unexpected) error /
errExit("wait");
}
}

numDead++;
printf("[%s] wait() returned child PID %ld (numDead=%d)\n",
currTime("%T"), (long) childPid, numDead);
}
}
––––––––––––––––––––––––––––––––––––––––––––––––––––– procexec/multi_wait.c